1. Field of the Invention
This invention relates to trays that are used by orthodontic practitioners to bond appliances to the teeth of an orthodontic patient. The invention is also related to methods for making such bonding trays.
2. Description of the Related Art
Orthodontic treatment involves movement of malpositioned teeth to desired locations in the oral cavity. Orthodontic treatment can improve the patient's facial appearance, especially in instances where the teeth are noticeably crooked or where the upper and lower teeth are out of alignment with each other. Orthodontic treatment can also enhance the function of the teeth by providing better occlusion during mastication.
One common type of orthodontic treatment involves the use of tiny, slotted appliances known as brackets. The brackets are fixed to the patient's teeth and an archwire is placed in the slot of each bracket. The archwire forms a track to guide movement of teeth to desired locations.
The ends of orthodontic archwires are often connected to small appliances known as buccal tubes that are, in turn, secured to the patient's molar teeth. In many instances, a set of brackets, buccal tubes and an archwire is provided for each of the patient's upper and lower dental arches. The brackets, buccal tubes and archwires are commonly referred to collectively as “braces”.
In many types of orthodontic techniques, the precise position of the appliances on the teeth is an important factor for helping to ensure that the teeth move to their intended final positions. For example, one common type of orthodontic treatment technique is known as the “straight-wire” technique, where the archwire lies in a horizontal plane at the conclusion of treatment. Consequently, the brackets must be correctly positioned at the beginning of treatment so that the teeth are properly aligned once the archwire straightens and lies in the horizontal plane. If, for example, a bracket is attached to the tooth at a location that is too close to the occlusal or outer tip of the tooth, the orthodontist using a straight-wire technique will likely find that the tooth in its final position is unduly intruded. On the other hand, if the bracket is attached to the tooth at a location closer to the gingiva than is appropriate, it is likely that the final position of the tooth will be more extruded than desired.
One technique for bonding orthodontic appliances to teeth is known as an indirect bonding technique. In the past, known indirect bonding techniques have often used a placement device or transfer apparatus having a shape that matches a configuration of at least part of the patient's dental arch. One type of transfer apparatus is often called a “transfer tray” or “indirect bonding tray” and typically has a cavity for simultaneously receiving a number of teeth. A set of appliances such as brackets are releasably connected to the tray at certain, predetermined locations.
During the use of a bonding tray for indirect bonding, an adhesive is typically applied to the base of each appliance by the orthodontist or a staff member. The tray is then placed over the patient's teeth and remains in place until such time as the adhesive hardens. Next, the tray is detached from the teeth as well as from the appliances, with the result that all of the appliances previously connected to the tray are now bonded to respective teeth at their intended, predetermined locations.
Indirect bonding trays are normally custom-made for each patient because the size and orientation of teeth can vary widely from one patient to the next. One method of making indirect bonding trays includes the steps of taking an impression of each of the patient's dental arches and then making a replica plaster or “stone” model from each impression. If desired, the teeth of the model can be marked with a pencil to assist in placing the brackets in ideal positions. Next, the brackets are temporarily bonded to the stone models. An indirect bonding tray is then made by placing matrix material over the model as well as over the brackets on the model. For example, a plastic sheet matrix material may be placed over the model and brackets and then heated in an oven under vacuum. As the plastic sheet material softens and as air in the oven is evacuated, the plastic sheet material assumes a configuration that precisely matches the shape of the replica teeth of the stone model and adjacent brackets. The plastic material is then allowed to cool and harden to form a tray.
While the state of the art with respect to indirect bonding trays has advanced in recent years, there is a continuing need to improve the accuracy of the placement of the appliances on the patient's teeth by such trays. Some orthodontists, for example, can detect very small differences (such as, for example, 0.5 mm) in positions of appliances with the naked eye and consequently may not be satisfied with the use of indirect bonding trays that do not consistently place appliances within such tolerances.